Medical instruments are currently in use that reduce the invasiveness and potential trauma previously associated with various medical procedures. One such procedure is the removal from the body of naturally occurring non-tissue objects referred to as stones, such as kidney stones and gallstones. Various medical retrieval devices are available which allow these stone-type objects to be removed from the body, for example via the urinary tract, without requiring major surgery. Typically, such instruments consist of two or more flexible elements. The flexible elements, such as wires, are formed in the shape of a resiliently collapsible basket, cage, grasper, or other entrapping mechanism. This basket is attached to a drive wire or actuation cable that passes through the lumen of a flexible sheath, which typically has an outer diameter of 1.9 to 3.0 Fr (1 Fr=0.33 mm) and is usually greater than 50 cm in length. The sheath and drive wire comprise the shaft portion of the device. At the proximal end of the shaft, the sheath and drive wire are attached to a multi-part handle, normally constructed of thermoplastic materials, which can typically be operated by the user with a single hand.
By manipulating the handle, the drive wire can be pulled back relative to the sheath, collapsing the basket as it retracts into the sheath. In this closed position, the sheath can be passed through the working channel of an endoscope to the proximity of the stone to be removed within the patient's body. By again manipulating the handle, which remains outside the endoscope and the patient's body, the basket is deployed from the end of the sheath, and expands to its open position. The device is then manipulated using the handle until the stone becomes enclosed within the basket. This manipulation may include advancing, withdrawing and/or rotating the basket in order to get the stone to pass between the flexible elements that comprise the basket. When the stone has been successfully engaged within the basket, the basket is partially closed to secure the stone within the basket wires, and the endoscope and the retrieval device containing the stone are then simultaneously removed from the body.
Many different basket configurations are in use for endoscopic object removal procedures. One conventional basket configuration uses a small diameter tube, typically 0.1 to 0.2 inches long, that extends beyond the distal end of the basket and inside of which the basket wires are joined at their distal end. Examples of such an extending tip basket configuration are shown in U.S. Patent Publ. No. 2003/0078593, and U.S. Pat. Nos. 4,927,426, 5,496,330, 6,168,603, and 6,190,394. Unfortunately, an extending basket tip has the disadvantage that the extending tip can cause trauma to body tissue, resulting in patient discomfort and bleeding, which not only may be injurious, but may also blur the physician's field of vision, thereby making the procedure more difficult or impossible. The extending tip is also a design disadvantage in many stone capture attempts (such as stone located in a calyx of the kidney) because the extended tip encounters structures so that the basket wires are hindered or prohibited from reaching the distal side of the stone.
The problems with extending tip designs for baskets have been addressed by baskets that are substantially tipless. Several types of tipless basket designs are known in the art as described, for example, in U.S. Pat. Nos. 4,590,938, 5,057,114, 5,989,266, 6,159,220, 6,224,612, 6,527,781, and 6,626,915, U.S. Patent Publ. Nos. 2003/0088254 and 2004/0133213 and U.S. patent application Ser. No. 10/831,986. These tipless baskets generally consist of multiple wire loops arranged in a manner similar to an eggwhip. The wire loops may or may not be connected at the basket's distal end, but the manner of connection is such that there is no substantial extending tip.
Tipless baskets are capable of retrieving stone-like objects, such as kidney stones, from difficult to access locations, such as the calices of the kidney. In order to access the kidney, a flexible endoscope, such as a flexible ureteroscope, is normally required. Flexible ureteroscopes are equipped with a mechanism for actively deflecting the tip of the ureteroscope in order to access locations that cannot be reached with a head-on approach, such as the upper and lower pole calices of the kidney. Typical flexible ureteroscopes can deflect up to about 180 degrees. Flexible ureteroscopes normally have one working channel, about 3.6 Fr in diameter, which is used for both irrigation fluid and working instruments, such as stone retrieval and lithotripsy devices. Irrigation is used to maintain clear visibility in the field of view, distend surrounding tissue to create an open working field, and to flush away small stone fragments resulting from lithotripsy procedures. Even with atraumatic tipless baskets, some bleeding often results from the manipulation of stones, particularly when the stone is impacted in the surrounding tissue. Small amounts of blood, when mixed with the saline used for irrigation, can significantly obscure the field of view.
During the course of a urological retrieval procedure, large stones are often fragmented using a lithotripsy device such as a laser. The laser fiber is passed through the working channel of the scope to the location of the stone in a similar manner to the retrieval device, and delivers laser energy to fragment the stone. One way that such a procedure is performed is that a tipless basket is first used to capture a stone located in a difficult to reach location (such as a lower pole calyx of the kidney) and then release the stone in a more accessible location for lithotripsy. The basket is then removed from the endoscope and replaced with the laser fiber, which is used to fragment the stone. The laser fiber is then withdrawn, and the tipless basket returned to the working channel of the scope to remove the larger fragments.
U.S. Pat. Nos. 6,325,807 and 6,398,791 disclose retrieval devices with an intermediate portion of the sheath near the distal end being more flexible than the rest of the sheath. This is accomplished by using several layers of different materials to construct the sheath. These prior art sheaths constructed of several layers of different materials are not practical for very small diameter sheaths, such as less than 1.7 Fr, because of the greater sheath wall thickness needed for the multiple layers. Additionally, the flexible portion of the sheath weakens the column strength of the sheath. This can make insertion of the device into the working channel of the ureteroscope through an endoscopic seal or adapter more difficult, and often requires a separate introducer to make the insertion possible. The weaker flexible portion of the sheath also is more susceptible to kinking or other damage that could result in a reduction in device functionality.
U.S. Patent Publ. No. 2004/0199048 discloses several designs intended to improve fluid flow in a working channel of a ureteroscope. One design is a basket without a sheath, where the basket is closed by withdrawing into the endoscope working channel. A second design is a basket with a ribbed or slotted sheath to increase fluid flow. A third design is to replace the sheath with a single thin control rod attached to a collar at the distal end for retracting the basket. A fourth design has a tapered sheath that has a larger distal portion to accommodate the basket, while the remainder of the sheath has a smaller, uniform diameter to improve fluid flow. These prior art designs proposed to improve fluid flow have several disadvantages. With a sheathless basket, the closed basket cannot be advanced from the ureteroscope, for example, to advance the basket in the closed state past an impacted stone and then open the basket beyond the stone. Additionally, control of basket opening and closing beyond the end of the ureteroscope is lost without a sheath. A ribbed sheath is of little practical advantage. Since standard polyimide sheaths used for stone baskets typically have wall thickness of only 0.003 inch or less, a ribbed design would have a negligible impact. A drive wire and control rod design has the disadvantage that it is inoperable outside of the endoscope making it very difficult to pretest the instrument prior to use. The tapered sheath does not have variable flexibility to match the articulating portion of a flexible ureteroscope to prevent loss of endoscope deflectability. Additionally, all of the embodiments disclosed in U.S. Patent Publ. No. 2004/0199048 use a 0.030 to 0.034 inch nitinol drive wire, which requires 2.3 to 2.6 Fr without a sheath.
An additional disadvantage of prior art tipless baskets is that multiple exchanges of retrieval and lithotripsy devices in the working channel of the ureteroscope lengthen the procedure and increase the chances of damage to the delicate instruments. The smallest of the commonly used laser fibers (272 μm, often referred to as 200 μm) has a sheath diameter of about 400 μm (1.2 Fr). It is only with this smallest size fiber and the smallest available tipless baskets (1.9 Fr) that both devices can simultaneously occupy the interior diameter of the working channel of a conventional ureteroscope. However, in this situation, the working channel is almost completely filled by the two devices, severely limiting irrigation flow. An unfortunate event that can occur is that a stone too large to remove intact cannot be released from the basket. When this happens and a laser fiber can be passed through the working channel, the stone can normally be fragmented so that the basket can be removed. However, if the sheath is too large to permit a laser fiber to be simultaneously passed through the working channel, the resolution of the situation can cause injury to the patient.
It would be desirable to provide a stone retrieval device for endoscopic retrieval procedures that provides improved fluid flow, permits sufficient flexible endoscope deflection, and is sized to share a single working channel with a laser fiber, without compromising device strength or functionality.